382. 链表随机节点

rand()就可以了

/**
 * Definition for singly-linked list.
 * struct ListNode {
 *     int val;
 *     ListNode *next;
 *     ListNode() : val(0), next(nullptr) {}
 *     ListNode(int x) : val(x), next(nullptr) {}
 *     ListNode(int x, ListNode *next) : val(x), next(next) {}
 * };
 */
class Solution {
public:
    long long length;
    ListNode* h;
    Solution(ListNode* head) {
        long long len = 0;
        ListNode* p = head;
        while(p)
        {
            len++;
            p = p->next;
        }
        length = len;
        h = head;
    }
    
    int getRandom() {
        long long cnt = 0;
        long long k = rand() % length;
        ListNode* p = h;
        while(p && cnt < k)
        {
            cnt++;
            p = p->next;
        }
        return p->val;
        

    }
};

/**
 * Your Solution object will be instantiated and called as such:
 * Solution* obj = new Solution(head);
 * int param_1 = obj->getRandom();
 */